Expansion pipe on two stroke marine engine possble ?

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Originally Posted by Fastjeff57

Question: How do those Formula One hydros run so damn fast without expansion chambers? All they have is a crude tuner built into the towerr.

Jeff

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Hey Jeff,

What appears to be a "crude" tuner is actually part of a folded expansion chamber that likely underwent thousands of hours of dyno time to develop. Remember that expansion chambers typically make power in a narrow powerband best suited to applications with VSD's or multi-speed transmissions. Outboard two-strokes require a much broader powerband that necessitates a totally different tuning approach. Never underestimate factory design features. Each and every single part was developed for a purpose. End users don't have a clue as to the time and $$$ invested to make those engines work.

Tim

3 into 1 pulse tuning ... almost as good as an expansion chamber

That's why there are so many triples and V-6's

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Originally Posted by Mark75H

3 into 1 pulse tuning ... almost as good as an expansion chamber

That's why there are so many triples and V-6's

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Agreed. Marine manufacturers use it for several reasons: Simple, light weight, wide power band, lowest cost. That's why my FE/850 engines use pulse tuning.

Tim

As a boat builder who is always looking for better handling and cornering, the FE boat we won a couple championships a couple years ago used a pulse tuning pipe which has all the attributes that Tim mentions but also makes the boat work better without heavy pipe(s) hanging off the back. This obviously has less impact on a bigger boat, but just replacing a steel bracket with an aluminum one on our CMH was detectable by the driver.

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Originally Posted by hydroplay

As a boat builder who is always looking for better handling and cornering, the FE boat we won a couple championships a couple years ago used a pulse tuning pipe which has all the attributes that Tim mentions but also makes the boat work better without heavy pipe(s) hanging off the back. This obviously has less impact on a bigger boat, but just replacing a steel bracket with an aluminum one on our CMH was detectable by the driver.

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Big time agreement with Sam - weight is a big issue for any boat. Given that your Tohatsu has pulse tuned exhaust already, you might consider running methanol and castor oil. You'll need only change carb jets, timing, and possibly a prop. Methanol has 20% more heat capacity than gasoline and something like 135 octane. This would be the simplest, lightest weight, and least cost way to increase power. You'll get more than a chamber for a whole lot less work.

Tim

3 into 1 exhaust tuning as mentioned on the other thread

is it possble some how to convert/modify a conventional expansion pipe into a " sliding pipe " ???
thanks
glen

Its commonly done at the lead in pipe by having one section slightly larger than the other, creating a slip joint.

It has also been done by having a second cone inside the final cone.

Another way to vary the tuning is water injection. Some current production PWC use water injection in their pipes.

Glen:

Almost every subject you have asked about has been covered in great detail in previous posts here on Boat Racing Facts.

If you will look at the top of the page you will see a white bar with what looks like a magnifying glass just to the right of the white bar. That is the "search" function. If you type in to the white bar the subject you are looking for and then click on the magnifying glass, you will find MUCH information and will not have to ask for it. As an example "water injection in expansion pipes, or sliding expansion chambers". You will find much information plus pictures which should be very helpful.

Then after you go thru what many folks have contributed, many of them answers to the same questions you are asking presently, you can target to get more specific answers that the search function has brought to mind.

No one here on BRF is unhappy with answering your questions, but most of the answers are already there for the reading and understanding, by just using the search function and enter the keyword/words you are interested in. I think you will find you will get more information that way as most folks have already spent much time previously answering the same questions by others.

Good Luck

i spoke to a mobile marine mechanic here in oz,and he has knows of some one that has fitted and modified a expansion pipe and he said that the ideal length from manifold to end of bleed of pipe should be approx 1,100 mm long.
well my modded fitted west coast marine pipe is about 900 mm long.
any way im taking the boat for a spin/testing on sunday,new redline race oil and redline synthetic gear box oil as well!!
cheers
glen